This invention relates to a process for the preparation of chemically modified soy proteins with improved functional properties. Currently, intensive research on food proteins is aimed to improve the functional properties of cheaper proteins so as to extend their processing adaptability and diversify their applications in food industries. The so-called functional property or functionality is any property of a substance, besides its nutritional ones, that affects its utilization. Such a property may be exemplified as foaming, whipping, emulsifying, gelling, fat and water absorption, adhesion, elasticity, film-forming or texturization, etc. Soybean protein is found to have many excellent intrinsic functional properties so that it is widely used as an ingredient to impart one or more functional characteristics of specific classes of formulated foods such as bakery, beverage, salad dressings, snacks, texturized meat analogs or extenders and many other processed foods. But the present commercialized soy protein concentrates or isolates can not completely replace casein or other animal proteins for food processing use. The reason is that soy protein is more or less denatured by organic solvent or heat treatment during early defatting process so that soy protein concentrates or isolates thus prepared from defatted soy flour will have a poor aqueous dispersibility and not reveal their deserved functionalities. Currently, some effective modifying methods available for improving the functional properties of soy proteins may comprise enzymatic partial hydrolysis of proteins by proteolytic enzymes and chemical sulfonation with sodium sulfite or succinylation with succinic anhydride. Specifically, the sulfonate or succinate anions covalently bonded onto cystine or lysine residues of proteins tend to increase in net negative charge of the polypeptide chains, which consequently alter the physiochemical character of the proteins resulting in an enhanced aqueous solubility and/or dispersibility and subsequent changes in emulsifying and foaming capacity. However, the enzymatic modifications may produce small bitter peptides. The chemical modifications as aforementioned may impair nutritional value of proteins. Hence, the sulfonated or succinylated proteins which are intended primarily as functional ingredients should not constitute a significant source of nutritive protein in fabricated foods.